diff --git a/src/cluster_legacy.c b/src/cluster_legacy.c
index d80144d3fc..e895bfca6f 100644
--- a/src/cluster_legacy.c
+++ b/src/cluster_legacy.c
@@ -69,7 +69,7 @@ int clusterAddSlot(clusterNode *n, int slot);
 int clusterDelSlot(int slot);
 int clusterDelNodeSlots(clusterNode *node);
 int clusterNodeSetSlotBit(clusterNode *n, int slot);
-void clusterSetPrimary(clusterNode *n, int closeSlots, int try_psync);
+static void clusterSetPrimary(clusterNode *n, int closeSlots, int full_sync_required);
 void clusterHandleReplicaFailover(void);
 void clusterHandleReplicaMigration(int max_replicas);
 int bitmapTestBit(unsigned char *bitmap, int pos);
@@ -2370,7 +2370,7 @@ int nodeUpdateAddressIfNeeded(clusterNode *node, clusterLink *link, clusterMsg *
     /* Check if this is our primary and we have to change the
      * replication target as well. */
     if (nodeIsReplica(myself) && myself->replicaof == node)
-        replicationSetPrimary(node->ip, getNodeDefaultReplicationPort(node), 1);
+        replicationSetPrimary(node->ip, getNodeDefaultReplicationPort(node), 0);
     return 1;
 }
 
@@ -2631,7 +2631,7 @@ void clusterUpdateSlotsConfigWith(clusterNode *sender, uint64_t senderConfigEpoc
              * just gets promoted to the new primary in the shard.
              *
              * If the sender and myself are in the same shard, try psync. */
-            clusterSetPrimary(sender, !are_in_same_shard, are_in_same_shard);
+            clusterSetPrimary(sender, !are_in_same_shard, !are_in_same_shard);
             clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG | CLUSTER_TODO_UPDATE_STATE | CLUSTER_TODO_FSYNC_CONFIG);
         } else if ((sender_slots >= migrated_our_slots) && !are_in_same_shard) {
             /* When all our slots are lost to the sender and the sender belongs to
@@ -3400,7 +3400,7 @@ int clusterProcessPacket(clusterLink *link) {
              * so we can try a psync. */
             serverLog(LL_NOTICE, "I'm a sub-replica! Reconfiguring myself as a replica of %.40s from %.40s",
                       myself->replicaof->replicaof->name, myself->replicaof->name);
-            clusterSetPrimary(myself->replicaof->replicaof, 1, areInSameShard(myself->replicaof->replicaof, myself));
+            clusterSetPrimary(myself->replicaof->replicaof, 1, !areInSameShard(myself->replicaof->replicaof, myself));
             clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG | CLUSTER_TODO_UPDATE_STATE | CLUSTER_TODO_FSYNC_CONFIG);
         }
 
@@ -4704,9 +4704,9 @@ void clusterHandleReplicaMigration(int max_replicas) {
         !(server.cluster_module_flags & CLUSTER_MODULE_FLAG_NO_FAILOVER)) {
         serverLog(LL_NOTICE, "Migrating to orphaned primary %.40s (%s) in shard %.40s", target->name,
                   target->human_nodename, target->shard_id);
-        /* We are migrating to a different primary, a total different replication
-         * history, so a full sync is required. */
-        clusterSetPrimary(target, 1, 0);
+        /* We are migrating to a different shard that has a completely different
+         * replication history, so a full sync is required. */
+        clusterSetPrimary(target, 1, 1);
     }
 }
 
@@ -5019,7 +5019,7 @@ void clusterCron(void) {
      * enable it if we know the address of our primary and it appears to
      * be up. */
     if (nodeIsReplica(myself) && server.primary_host == NULL && myself->replicaof && nodeHasAddr(myself->replicaof)) {
-        replicationSetPrimary(myself->replicaof->ip, getNodeDefaultReplicationPort(myself->replicaof), 1);
+        replicationSetPrimary(myself->replicaof->ip, getNodeDefaultReplicationPort(myself->replicaof), 0);
     }
 
     /* Abort a manual failover if the timeout is reached. */
@@ -5412,7 +5412,7 @@ static inline void removeAllNotOwnedShardChannelSubscriptions(void) {
 
 /* Set the specified node 'n' as primary for this node.
  * If this node is currently a primary, it is turned into a replica. */
-void clusterSetPrimary(clusterNode *n, int closeSlots, int try_psync) {
+static void clusterSetPrimary(clusterNode *n, int closeSlots, int full_sync_required) {
     serverAssert(n != myself);
     serverAssert(myself->numslots == 0);
 
@@ -5426,7 +5426,7 @@ void clusterSetPrimary(clusterNode *n, int closeSlots, int try_psync) {
     myself->replicaof = n;
     updateShardId(myself, n->shard_id);
     clusterNodeAddReplica(n, myself);
-    replicationSetPrimary(n->ip, getNodeDefaultReplicationPort(n), try_psync);
+    replicationSetPrimary(n->ip, getNodeDefaultReplicationPort(n), full_sync_required);
     removeAllNotOwnedShardChannelSubscriptions();
     resetManualFailover();
 
@@ -6357,9 +6357,9 @@ void clusterCommandSetSlot(client *c) {
                       "Lost my last slot during slot migration. Reconfiguring myself "
                       "as a replica of %.40s (%s) in shard %.40s",
                       n->name, n->human_nodename, n->shard_id);
-            /* We are migrating to a different primary, a total different replication
-             * history, so a full sync is required. */
-            clusterSetPrimary(n, 1, 0);
+            /* We are migrating to a different shard that has a completely different
+             * replication history, so a full sync is required. */
+            clusterSetPrimary(n, 1, 1);
             clusterDoBeforeSleep(CLUSTER_TODO_SAVE_CONFIG | CLUSTER_TODO_UPDATE_STATE | CLUSTER_TODO_FSYNC_CONFIG);
         }
 
@@ -6568,7 +6568,7 @@ int clusterCommandSpecial(client *c) {
          * If the instance is a primary, it is an empty primary.
          * If the instance is a replica, it had a totally different replication history.
          * In these both cases, myself as a replica has to do a full sync. */
-        clusterSetPrimary(n, 1, 0);
+        clusterSetPrimary(n, 1, 1);
         clusterBroadcastPong(CLUSTER_BROADCAST_ALL);
         clusterDoBeforeSleep(CLUSTER_TODO_UPDATE_STATE | CLUSTER_TODO_SAVE_CONFIG);
         addReply(c, shared.ok);
diff --git a/src/replication.c b/src/replication.c
index 76fde030ab..2e353df1d1 100644
--- a/src/replication.c
+++ b/src/replication.c
@@ -3723,7 +3723,7 @@ int cancelReplicationHandshake(int reconnect) {
 }
 
 /* Set replication to the specified primary address and port. */
-void replicationSetPrimary(char *ip, int port, int try_psync) {
+void replicationSetPrimary(char *ip, int port, int full_sync_required) {
     int was_primary = server.primary_host == NULL;
 
     sdsfree(server.primary_host);
@@ -3752,14 +3752,16 @@ void replicationSetPrimary(char *ip, int port, int try_psync) {
 
     /* Before destroying our primary state, create a cached primary using
      * our own parameters, to later PSYNC with the new primary. */
-    if (was_primary && try_psync) {
+    if (was_primary && !full_sync_required) {
         replicationDiscardCachedPrimary();
         replicationCachePrimaryUsingMyself();
     }
 
-    /* If try_psync is 0, it means the caller requested that psync not be
-     * performed, dropping the cached primary. */
-    if (!try_psync) {
+    /* If full sync is required, drop the cached primary. Doing so increases
+     * this replica node's election rank (delay) and reduces its chance of
+     * winning the election. If a replica requiring a full sync wins the
+     * election, it will flush valid data in the shard, causing data loss. */
+    if (full_sync_required) {
         replicationDiscardCachedPrimary();
     }
 
@@ -3900,7 +3902,7 @@ void replicaofCommand(client *c) {
         }
         /* There was no previous primary or the user specified a different one,
          * we can continue. */
-        replicationSetPrimary(c->argv[1]->ptr, port, 1);
+        replicationSetPrimary(c->argv[1]->ptr, port, 0);
         sds client = catClientInfoString(sdsempty(), c);
         serverLog(LL_NOTICE, "REPLICAOF %s:%d enabled (user request from '%s')", server.primary_host,
                   server.primary_port, client);
@@ -4909,7 +4911,7 @@ void updateFailoverStatus(void) {
                       server.target_replica_port);
             server.failover_state = FAILOVER_IN_PROGRESS;
             /* If timeout has expired force a failover if requested. */
-            replicationSetPrimary(server.target_replica_host, server.target_replica_port, 1);
+            replicationSetPrimary(server.target_replica_host, server.target_replica_port, 0);
             return;
         } else {
             /* Force was not requested, so timeout. */
@@ -4952,6 +4954,6 @@ void updateFailoverStatus(void) {
         serverLog(LL_NOTICE, "Failover target %s:%d is synced, failing over.", server.target_replica_host,
                   server.target_replica_port);
         /* Designated replica is caught up, failover to it. */
-        replicationSetPrimary(server.target_replica_host, server.target_replica_port, 1);
+        replicationSetPrimary(server.target_replica_host, server.target_replica_port, 0);
     }
 }
diff --git a/src/server.h b/src/server.h
index 2acf78e1e1..6ee4d5e05e 100644
--- a/src/server.h
+++ b/src/server.h
@@ -3020,7 +3020,7 @@ void replicationStartPendingFork(void);
 void replicationHandlePrimaryDisconnection(void);
 void replicationCachePrimary(client *c);
 void resizeReplicationBacklog(void);
-void replicationSetPrimary(char *ip, int port, int try_psync);
+void replicationSetPrimary(char *ip, int port, int full_sync_required);
 void replicationUnsetPrimary(void);
 void refreshGoodReplicasCount(void);
 int checkGoodReplicasStatus(void);
diff --git a/tests/unit/cluster/replica_migration.tcl b/tests/unit/cluster/replica_migration.tcl
index e3927027f9..0c81fe54bf 100644
--- a/tests/unit/cluster/replica_migration.tcl
+++ b/tests/unit/cluster/replica_migration.tcl
@@ -19,18 +19,18 @@ start_cluster 4 4 {tags {external:skip cluster} overrides {cluster-node-timeout
         assert_equal {1024} [R 0 get key_991803]
     }
 
-    test "Write some data to primary 4, slot 0, make a big repl_offset" {
+    test "Write some data to primary 3, slot 0, make a big repl_offset" {
         for {set i 0} {$i < 10240} {incr i} {
             R 3 incr key_977613
         }
         assert_equal {10240} [R 3 get key_977613]
     }
 
-    test "If a replica has not completed sync, it can not do the failover" {
-        # 10s, make sure primary 1 will hang in the save
+    test "If a replica has not completed full sync, the offset is 0 and the rank is the lowest" {
+        # 10s, make sure primary 0 will hang in the save.
         R 0 config set rdb-key-save-delay 100000000
 
-        # Move the slot 0 from primary 4 to primary 1
+        # Move the slot 0 from primary 3 to primary 0
         set addr "[srv 0 host]:[srv 0 port]"
         set myid [R 3 CLUSTER MYID]
         set code [catch {
@@ -40,15 +40,15 @@ start_cluster 4 4 {tags {external:skip cluster} overrides {cluster-node-timeout
             fail "valkey-cli --cluster rebalance returns non-zero exit code, output below:\n$result"
         }
 
-        # Let primary 4's primary and replica can convert to replicas when
-        # they lost the last slot.
+        # Validate that shard 3's primary and replica can convert to replicas after
+        # they lose the last slot.
         R 3 config set cluster-replica-validity-factor 0
         R 7 config set cluster-replica-validity-factor 0
         R 3 config set cluster-allow-replica-migration yes
         R 7 config set cluster-allow-replica-migration yes
 
-        # Shutdown the primary 1
-        catch {R 0 shutdown nosave}
+        # Shutdown the primary 0.
+        catch {R 0 shutdown}
 
         # Wait for the replica become a primary, and make sure
         # the other primary become a replica.
@@ -63,14 +63,14 @@ start_cluster 4 4 {tags {external:skip cluster} overrides {cluster-node-timeout
             fail "Failover does not happened"
         }
 
-        # Make sure 3 / 7 get the lower rank and offset is 0.
+        # Make sure 3 / 7 get the lower rank and the offset is 0.
         verify_log_message -3 "*Start of election*offset 0*" 0
         verify_log_message -7 "*Start of election*offset 0*" 0
 
         # Make sure the right replica get the higher rank.
         verify_log_message -4 "*Start of election*rank #0*" 0
 
-        # Make sure the key is exists and consistent.
+        # Make sure the key exists and is consistent.
         R 3 readonly
         R 7 readonly
         wait_for_condition 1000 50 {
@@ -94,7 +94,7 @@ start_cluster 4 4 {tags {external:skip cluster} overrides {cluster-node-timeout
         assert_equal {1024} [R 0 get key_991803]
     }
 
-    test "Write some data to primary 4, slot 0, make a big repl_offset" {
+    test "Write some data to primary 3, slot 0, make a big repl_offset" {
         for {set i 0} {$i < 10240} {incr i} {
             R 3 incr key_977613
         }
@@ -102,16 +102,16 @@ start_cluster 4 4 {tags {external:skip cluster} overrides {cluster-node-timeout
     }
 
     test "A old replica use CLUSTER REPLICA get a zero offset before the full sync is completed" {
-        # 10s, make sure primary 1 will hang in the save
+        # 10s, make sure primary 0 will hang in the save.
         R 0 config set rdb-key-save-delay 100000000
 
-        # Let the replica do the replicate with primary 1.
+        # Let the replica do the replicate with primary 0.
         R 7 config set cluster-replica-validity-factor 0
         R 7 config set cluster-allow-replica-migration yes
         R 7 cluster replicate [R 0 cluster myid]
 
-        # Shutdown the primary 1.
-        catch {R 0 shutdown nosave}
+        # Shutdown the primary 0.
+        catch {R 0 shutdown}
 
         # Wait for the replica become a primary.
         wait_for_condition 1000 50 {
@@ -127,7 +127,7 @@ start_cluster 4 4 {tags {external:skip cluster} overrides {cluster-node-timeout
         verify_log_message -4 "*Start of election*rank #0*" 0
         verify_log_message -7 "*Start of election*offset 0*" 0
 
-        # Make sure the key is exists and consistence.
+        # Make sure the key exists and is consistent.
         R 7 readonly
         wait_for_condition 1000 50 {
             [R 4 get key_991803] == 1024 &&